MEDICARE PART D (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Other current assets	$ 3,965	$ 3,564
Trade accounts payable and accrued expenses	(3,719)	(3,067)
Other long-term assets	1,555	1,375
Other long-term liabilities	(992)	(581)
Risk Corridor Settlement
Segment Reporting Information [Line Items]
Other current assets	10	15
Trade accounts payable and accrued expenses	(63)	(103)
Net current liability	(53)	(88)
Other long-term assets	26	7
Other long-term liabilities	(134)	(89)
Net long-term liability	(108)	(82)
Total net liability	(161)	(170)
CMS Subsidies/ Discounts
Segment Reporting Information [Line Items]
Other current assets	333	172
Trade accounts payable and accrued expenses	(1,285)	(503)
Net current liability	(952)	(331)
Other long-term assets	0	0
Other long-term liabilities	0	0
Net long-term liability	0	0
Total net liability	$ (952)	$ (331)